Stereoselectivity in Reactions of 1,2-Dioxy-Substituted Radicals under Chelation Control: An Unexpected Result†
Michèle Gerster
Université de Fribourg, Institut de Chimie Organique Pérolles, CH-1700 Fribourg (Switzerland) Fax: Int. code +(37)29 97 39 e-mail: [email protected]
Search for more papers by this authorDr. Kurt Schenk
Université de Lausanne, Institut de Cristallographie BSP, CH-1015 Lausanne (Switzerland)
Search for more papers by this authorCorresponding Author
Prof. Philippe Renaud
Université de Fribourg, Institut de Chimie Organique Pérolles, CH-1700 Fribourg (Switzerland) Fax: Int. code +(37)29 97 39 e-mail: [email protected]
Université de Fribourg, Institut de Chimie Organique Pérolles, CH-1700 Fribourg (Switzerland) Fax: Int. code +(37)29 97 39 e-mail: [email protected]Search for more papers by this authorMichèle Gerster
Université de Fribourg, Institut de Chimie Organique Pérolles, CH-1700 Fribourg (Switzerland) Fax: Int. code +(37)29 97 39 e-mail: [email protected]
Search for more papers by this authorDr. Kurt Schenk
Université de Lausanne, Institut de Cristallographie BSP, CH-1015 Lausanne (Switzerland)
Search for more papers by this authorCorresponding Author
Prof. Philippe Renaud
Université de Fribourg, Institut de Chimie Organique Pérolles, CH-1700 Fribourg (Switzerland) Fax: Int. code +(37)29 97 39 e-mail: [email protected]
Université de Fribourg, Institut de Chimie Organique Pérolles, CH-1700 Fribourg (Switzerland) Fax: Int. code +(37)29 97 39 e-mail: [email protected]Search for more papers by this authorThis work was supported by the Swiss National Science Foundation (Project CHiral2, grant no 2027-44′234.95). M. G. is very grateful to the Stipendienfonds der Chemischen Industrie Basel for financial support. We thank Ciba-Geigy (Marly, Switzerland) for the microanalysis.
Graphical Abstract
The strong pyramidalization of the radical intermediates (shown on the right) is the reason why anti Cram chelation products are obtained in the reduction of 1,2-dialkyl-1,2-dioxy-substituted radicals, even though a chelate is formed. The main diastereoisomer results from an attack syn to the large substituent R2. R1 CH2CHCHCH2SnBu3, R2 tBu, R para-methoxyphenyl.
References
- 1 P. Renaud, M. Gerster, J. Am. Chem. Soc. 1995, 117, 6607–6608.
- 2 Since the publication of our preliminary results [1], we have discovered that it is more convenient to use Me3Al instead of Et2AlCl/Na2CO3 to prepare the aluminum alkoxide.
- 3 Reviews on the stereoselectivity of radical reactions: N. A. Porter, B. Giese, D. P. Curran, Acc. Chem. Res. 1991, 24, 296–304; W. Smadja, Synlett 1994, 1–26; D. P. Curran, N. A. Porter, B. Giese, Stereochemistry of Radical Reactions, VCH, Weinheim, 1996.
- 4 For stereoselective reactions based on 1-oxy radicals, see: B. Giese, W. Damm, J. Dickhaut, F. Wetterich, S. Sun, D. P. Curran, Tetrahedron Lett. 1991, 32, 6097–6100; B. Giese, B. Carboni, T. Göbel, R. Muhn, F. Wetterich, Tetrahedron Lett. 1992, 33, 2673–2676.
- 5
For chelation control in radical reactions, see:
Y. Guindon,
J.-F. Lavallée,
M. Llinas-Brunet,
G. Horner,
J. Rancourt,
J. Am. Chem. Soc.
1991,
113, 9701–9702;
Y. Guindon,
B. Guérin,
C. Chabot,
N. Mackintosh,
W. W. Ogilvie,
Synlett
1995,
449–451;
H. Nagano,
Y. Kuno,
J. Chem. Soc. Chem. Commun.
1994,
987–988;
T. Toru,
Y. Watanabe,
M. Tsusaka,
Y. Ueno,
J. Am. Chem. Soc.
1993,
115, 10464–10465;
M. Kito,
T. Sakai,
K. Yamada,
F. Matsuda,
H. Shiramana,
Synlett
1993,
158–162;
T. Gillmann,
Tetrahedron Lett.
1993,
34, 607–610;
Y. Yamamoto,
S. Onuki,
M. Yumoto,
N. Asao,
J. Am. Chem. Soc.
1994,
116, 421–422;
M. Kawatsura,
F. Matsuda,
H. Shirahama,
J. Org. Chem.
1994,
59, 6900–6901;
A. G. Molander,
J. A. McKie,
J. Org. Chem.
1995,
60, 872–882;
H. Urabe,
K. Yamashita,
K. Suzuki,
K. Kobayashi,
F. Sato,
J. Org. Chem.
1995,
60, 3576–3577;
J. Hongliu,
R. Radinov,
N. A. Porter,
J. Am. Chem. Soc.
1995,
117, 11029–11030;
M. P. Sibi,
C. J. Jasperse,
J. Ji,
J. Am. Chem. Soc.
1995,
117, 10779–10780;
H. Stadtmüller,
P. Knochel,
Synlett
1995,
463–464.
M. P. Sibi,
J. Ji,
Angew. Chem.
1996,
108, 198–200;
10.1002/ange.19961080215 Google ScholarAngew. Chem. Int. Ed. Engl. 1996, 35, 190–192.
- 6 K. S. Feldman, H. M. Berven, P. H. Weinreb, J. Am. Chem. Soc. 1993, 115, 11364–11369.
- 7 R. N. Saisic, R. Matovic, Z. Cekovic, Gazz. Chim. Ital. 1991, 121, 325–328.
- 8 Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-179-89. Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: Int. code +(1223) 336-033; e-mail: [email protected]).
- 9 The preliminary 13C NMR study supports the formation of a chelate. Details will be published in a forthcoming full paper.
- 10 The reaction with like(lk) topicity affords the unlike(u) product and vice versa.
- 11 J. E. Eksterowicz, K. N. Houk, Tetrahedron Lett. 1993, 34, 427–430; W. Damm, J. Dickhaut, F. Wetterich, B. Giese, Tetrahedron Lett. 1993, 34, 431–434.
- 12 R. D. McKelvey, T. Sugarawa, H. Iwamura, Magn. Reson. Chem. 1985, 23, 330–334; Y.-D. Wu, K. N. Houk, J. Am. Chem. Soc. 1992, 114, 1656–1661.
- 13 Very recently it was found that the stereoselectivity of 1-amino-substituted cyclic radicals was strongly dependent of the nature of the R group attached at the radical center. An explanation based on pyramidalization of the reactive center in the transition state was proposed: D. Crich, S. Natarajan, J. Org. Chem. 1995, 60, 6237–6241.
- 14 D. J. Cram, F. A. A. Elhafez, J. Am. Chem. Soc. 1952, 74, 5828–5835; D. J. Cram, K. R. Kopecky, J. Am. Chem. Soc. 1959, 81, 2748–2755; D. J. Cram, D. R. Wilson, J. Am. Chem. Soc. 1963, 85, 1245–1249; J. H. Stocker, P. Sidisunthorn, B. M. Benjamin, C. J. Collins, J. Am. Chem. Soc. 1960, 82, 3913–3918; for a review, see: E. L. Eliel, S. H. Wilen, Stereochemistry of Organic Compounds, Wiley, New York, 1994.
- 15 Preliminary experiments have shown that the 2-tert-butyl-1-methyloxiranyl radical reacts preferentially with ul topicity that is syn to the tert-butyl group. For reaction with monosubstituted oxiranyl radicals, see: F. E. Ziegler, P. G. Harran, Tetrahedron Lett. 1993, 34, 4505–4508.
- 16 Syn bromination of 2-substituted aziridinyl radicals has been reported: F. E. Ziegler, M. Belena, J. Org. Chem. 1994, 59, 7962–7967.
- 17 For a recent result that may fit in this category, see: H. Urabe, K. Kobayashi, F. Sato, J. Chem. Soc. Chem. Commun. 1995, 1043–1044. See also J. O. Metzger, K. Schwarzkopf, W. Saak, S. Pohl, Chem. Ber. 1994, 127, 1069–1073.
